Compacting of paper and similar fiber webs



June 2, 1970 J. M. FUTCH, JR 3, 1

COMPACTING OF PAPER AND SIMILAR FIBER WEBS' I Filed Feb. 27, 1967 I 2Sheets-Sheet 1 v IO FIG.I

JuneZ, 1970 J.- M. FUTCH, JR 3,515,333

COMPACTING OF PAPER AND SIMILAR FIBER WEBS I Filed Feb. 27. 1967 2Sheets- Sheet 2 FIG. 2

United States Patent 3,515,633 COMPACTING OF PAPER AND SIMILAR FIBERVVEBS James M. Futch, Jr., Yonges, S.C., assignor to Clupak, Inc., NewYork, N.Y., a corporation of Delaware Filed Feb. 27, 1967, Ser. No.618,792 Int. Cl. D21f 3/02 U.S. Cl. 162206 5 Claims ABSTRACT OF THEDISCLOSURE Process and apparatus for compacting paper and similarcellulosic-fiber-containing webs, to enhance the stretchability andtoughness thereof, in a pressure nip at moisture contents within arange. To achieve such compaction the pressure nip includes conventionalresilient surface element and a special hard surface element the surfaceof which has a combination of characteristics such that it exerts verylow drag with respect to the web at the moisture contents involved. Thecompaction of the web is immediately followed by machine glazing.

BACKGROUND OF THEINVENTION The field of the present invention is thecompaction of fibrous webs such as paper and the like in which thefibers or a substantial percentage of the fibers of which the web iscomposed are natural cellulosic fibers which have been liberated to formpulp by chemical, semichemical or mechanical processes. A major reasonfor the compaction of such webs is to impart to them toughness andstretchability greater than that of a similar web which has not beencompacted.

It is known in the prior art to compact webs of paper and similarproducts by passing the web through a pressure nip which simultaneouslyexerts on the web forces acting normal to the general web surfaces andforces acting parallel to the general web surfaces. In this regardreference is made, for example, to U.S. Pat. No. 2,624,- 245 to S. L.Cluett and U.S. Pat No. 3,122,469 to Fred H. Freuler. It is also knownto compact asbestos fiber Webs in a manner such as is described in U.S.Pat. No. 3,148,- 108 to S. -L. Cluett. In these known processes theforces which act parallel to the general web surfaces in the pressurenip serve to rearrange and/or distort fibers within the web and whilesuch action is known to produce various effects in the web a primarilyimportant commercial effect is to impart to the web a definite degree ofstretch which is recoverable in the web after drying and which is inexcess, in the direction in which such forces were applied, of thestretch which a similar web would have had it not been subjected to theaction of the pressure nip. An important commercial advantage of suchadditional recoverable stretch is that the treated paper or other webexhibits substantially greater toughness than is exhibited by anuntreated web.

It has been thought that the amount of compaction that could be impartedto a fibrous paper web was controlled by the water to fiber ratio of theweb at the time the same was passed through the pressure nip. The CluettU.S. Pat. No. 2,624,245 indicates that at a ratio of about 1:1 (byweight) little or no compaction occurred on the first pass through thecompacting device which, as disclosed in said patent, utilizes thepressure nip between the surface of an elastomeric material and a heatedhard-surface pressure roll. However, said patent indicates thatcompaction will be obtained with further passes through the same orsimilar compacting devices as a result of the removal of water whichoccurs in the earlier passes. It has been found from commercialexperience in the prior art practice of compaction, usually in a single3,515,633 Patented June 2, 1970 pass, that a water to fiber ratio offrom about 0.5 21.0 to not more than about 0.65: 1.0 produces the bestbalance of compaction and smoothness of the final product.

It is well known that paper webs are formed on the forming screen of acylinder mould or Fourdrinier machine by removing water from asuspension of fiber in water by drainage of water through the screenboth with and without promotion by suction. The surface tension of thewater as the web is thus consolidated causes the fibers to be pulledinto a wet mat. This wet mat, upon further removal of water as bypressing and drying by evaporation, is additionally densified andstrengthened because of the formation between the fibers of chemicalbonds generally thought to be hydrogen bonds between the hydroxyl groupsof cellulose molecules.

Typically a web of paper leaves the forming screen with a moisturecontent of about by weight which corresponds with a water to fiber ratioof about 4: 1. This moisture content is reached when air has struckthrough the web just before it leaves the forming screen. It is apparentat such moisture content there is a substantial quantity of water on thesurfaces of the fibers in addition to the quantity of water with whichthe fibers are saturated. In the commercial practice of compaction ofpaper webs as discussed above it has been regarded as essential toreduce the moisture content of the web to the level discussed above bypressing and by evaporative drying before the compaction is performed.

Although the exact function of water during the compaction process wasunkown it was believed that sufficient water had to be removed not onlyto provide unfilled voids in the fibrous mat but also to permitsubstantial bonding to occur between fibers before compaction. That is,it was believed that bonding of the type which occurs at a moisturecontent below fiber saturation had first to be established before thefibers could be curled and compacted between the established bond sites.It was believed that at moisture contents above fiber saturationinsuflicient fiber bonds had been formed so that the net effect ofcompaction at such moisture contents would be simply to consolidate theweb creating a higher basis weight but imparting to the web little or noadditional recoverable stretch.

SUMMARY OF THE INVENTION In contradistinction to the beliefs aforesaidthe present inventor has discovered that fibrous webs can be compactedat moisture contents very substantially above fiber saturation, i.e. inthe range of from about 1:1 to about 3:1 water to fiber ratio, byweight, and that such compaction yields recoverable extensibility in thefinally dried web which generally corresponds with the amount of compaction just as is the case in compaction at the lower moisture contentsheretofore used. The present inventor has discovered that the limitingfactor in the prior commercial as well as experimental methods ofcompaction has been the relative drag between the wet web and the hardsurface element in the compacting device instead of the factorsheretofore thought to be limiting.

Efforts have been made in the past to reduce the drag of the wet webupon the polished metal surfaces used in the compaction process. Thesehave included various treatments of the metal surface primarilyconsisting of forming a matte finish of carefully limited degree on apreviously highly polished metal surface. Also, extensive studies havebeen made to establish empirical optimum temperatures for the metalsurface in the manufacture of particular products to obtain the benefitof lubricating effect of a layer of steam. Also, commercial operationshave quite frequently been improved by addition of lubricants such aswater emulsions of silicone oils. These earlier efforts with the web atmoisture contents in the range now made possible by the presentinvention.

The present invention makes use of hard pressure surfaces having verylittle tendency to adhere to wet cellulosic webs because they have lowcoefiicients of friction with respect to such webs. Examples of suchsurfaces are surfaces made wholly or in part of Teflon resin or otherresins having similar characteristics or metal surfaces having smallconvex nodules formed thereon and closely and quite uniformlydistributed over the entire working portion of the surface.

Hard surfaces of the types suitable for the present inventioncharacteristically have quite high contact angles with water, haverelatively low coeflicients of static friction with respect to wetcellulosic sheet material and exhibit very low or in some cases nodetectable tendency to pick fibers from freshly formed wet cellulosicsheet material. As will be more fully explained below certain of thesuitable surfaces are preferred for practical reasons such as durabilityunder commercial production conditions.

The ability to compact fibrous webs at the moisture contents madepracticable by the present invention affords many advantages some ofwhich have been sought after from the beginning of commercial practiceof compaction in accordance with the prior art. For example it hasalways been necessary to subject a web of paper first, to dewatering inthe wet press section of a papermaking machine and second, to asubstantial amount of evaporative drying, as on the first several heateddryer drums of the machine, to bring the moisture content down to eventhe highest level at which prior art compaction has been possible. Thepartial evaporative drying on dryer drums is inherently non-uniformacross the width of the web whereby prior-art-compacted paper webs havevery frequently exhibited varying degrees of compaction and/or surfaceappearance in the zones of differing moisture content. The moisturecontent of a paper web as it leaves a wet press or the wet press sectionis much more uniform than it is likely to be after the web has passedover the first several dryer drums. Therefore, compaction of the paperimmediately after it leaves a wet press or a wet press section has longbeen regarded as desirable but impossible of achievement prior to thepresent invention.

Another long felt need in the paper industry has been a machine glazedpaper with the enhanced stretch and toughness characteristics of theprior-art-compacted papers. This has not been possible since the papermust have a moisture content of at least 1:1 water to fiber ratio to bemachine glazed whereas the prior art compaction could only be carriedout at a much lower moisture content. Obviously the paper could notfirst be glazed and then compacted because the compaction process wouldadversely afiect the glam finish. With the present invention the papermay 'be compacted at a moisture content so high that it may be machineglazed after compaction. Thus, this invention provides a new and highlydesired product for the paper industry.

DESCRIPTION OF DRAWINGS FIG. 1 is an apparatus constructed in accordancewith and designed to carry out the process of the present invention;

FIG. 2 is an alternate arrangement of the apparatus of FIG. 1; and

FIG. 3 is a detail view of the pressure nip of a mechanical compactorfor fibrous webs.

FIG. 4 is a fragmentary view of the compactor roll showing surfacedeformation generally.

4 DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows one embodimentof an apparatus adapted for the practice of the present invention and inthis figure the compactor is illustrated in such a position that itoperates upon a web of paper immediately after it emerges from a wetpress or the wet press section of a papermaking machine. In this figurethere is shown a head box 10 and a Fourdrinier screen 11 as well as asuction box 12 and the various rollers (table rolls 13, couch roll 14,takeup roll 15, guide roll 16 and idlers 17, 18 and 19) which comprisethe basic elements of the forming section 20 of a typical papermakingmachine.

A web of paper 22 is shown leaving the Fourdrinier screen 11 at thecouch roll 14. The web 22 typically leaves the Fourdrinier screen at awater to fiber ratio of about 4: 1 by Weight, although this varies tosome extent in either direction depending upon the grade of paper andthe characteristics of a particular installation. Typically the web 22passes from the Fourdrinier screen to the first press in a wet presssection which is designated generally by the reference numeral 23. Thefunction of the press section 23 is to remove some of the water from theweb 22 and to assist in forming it into a suitable coherent structure byconsolidation and smoothing. Only one wet press is shown although itWill be understood that two or three presses are usually included in atypical wet press section. Each press ordinarily includes a press feltor fabric 24 on the upper surface of which the web 22 is carried throughthe press. The press also includes a pair of generally vertically alinedpress rolls 25 which are pressed together upon the web 22 and felt 24with force appropriate for squeezing of water from the web 22 and forsmoothing and consolidation of the web as mentioned above.

A web of paper will leave a typical wet press or wet press section at aquite high moisture content, for example a water to fiber ratio of about1:1 to about 3:1 depending upon the efliciency of the press or number ofpresses as well as upon the particular grade of paper beingmanufactured. Moisture contents in the range of those exhibited by websleaving the typical Wet press 01 wet press section are thus veryconsiderably in excess of those at which compaction of paper has beenpracticed in accordance with the prior art. Therefore it has beennecessary in the past to run the web over a sufficient number ofevaporative dryers, such as those generally indicated at 30 in FIG. 1 tolower the moisture content to ratios substantially below 1:1, usuallywithin a range of about 0.511 to about 0.65:1.

However the present invention makes it possible to compact paper orother cellulosic fibrous webs at moisture contents within the range atwhich a web typically leaves the wet press section as Well as at lowermoisture contents. Thus, as shown in FIG. 1, a compactor unit 40 isinstalled in a position ahead of the first heated drum 31 of the dryersection 30. This is made possible in accordance with the presentinvention by the utilization in the compactor 40 of a hard surfaceelement having a combination of characteristics as will be described ingreater detail hereinbelow. From the compactor unit 40 the compacted web22 is passed to the first dryer drum 31 of the dryer section 30. Thedryer section 30' includes as is conventional, a plurality of dryerdrums 31, upper and lower dryer felts or fabrics 32 and the usualguiding and tensioning rolls 33, 34 and 35 for the felts. The felts 32serve to hold the web 22 against the dryer drums. In some instancesrolls 35 are heated to remove some moisture from the dryer felts 32.From the dryer section 30 the compacted and dried web may be conductedas desired to conventional equipment such as calenders, reels and thelike, not shown.

In FIG. 1 the dryer section 30 has been broken away to indicate that anydesired number of dryer drums may be used. Frequently the dryer sectionis made up of two or more groups of dryer drums, each group having itsown conventional arrangement of dryer felts or fabrics and in someinstances a size press or the like is positioned between groups of dryerdrums. Any such arrangements may be used with the present invention.However, it should be observed that with the present invention as wellas with prior art compacting equipment care should.

be exercised to keep longitudinal tension on the Web 22 in the dryersection 30 low enough that the desired portion of the enhancedstretchability imparted to the web by the compactor 40 will be retainedin the finally dried; web 22.

In FIG. 2 an embodiment of the invention is shown for the production ofcompacted machine-glazed paper. In this figure a compactor 240 is shownpositioned just ahead of a Yankee dryer section 251. The compactor 240may be identical with the compactor 40 shown in FIG. 1 and it will bedescribed in greater detail below. A web of paper 222 is shown passingthrough the compactor 240 and from there to the Yankee dryer section251.

The Yankee dryer section 251 includes a large-diameter heated drum 252which has a highly polished surface for contact with the web 222. Thecompacted web 222 is guided from the compactor 240 onto the drum 252 bya pressure roll 253 which assures tight contact of one surface of theWeb with the highly polished surface of drum 252. A conventional Yankeedryer felt 254 and conventional tension and guiding rolls 255, 256therefor serves to hold the web 222 in contact with a substantialportion of the periphery of the drum 252 as is customary in Yankee dryersections. The compacted dried web 222 is guided by a roll 257 to a reel258.

For machine glazing of paper on a Yankee dryer, as shown in FIG. 2, oron a stack or heated dryer rolls which press the paper between them likea calender stack as is sometimes used, it is known that the paper musthave. a moisture content of at least about 50%, that is a Water to fiberratio by weight of about 1:1, at the time it first comes into contactwith the dryer drum surface on which it is to be glazed. When themoisture content is below this range the paper typically breaksprematurely away from the drum surface and dries without attaining thedesired glossy finish. In the proper operating range for glazing thepaper will adhere firmly to the drum surface and will remain so adheredlong enough that the surface of the paper will take on the desiredhighly polished permanent finish which is a mirror image of the surfaceof the drum.

With the present invention a compactor 240 is provided for the firsttime which is capable of compacting paper at water to fiber ratios wellis in excess of 1:1 whereby the web 222 may be introduced to thecompactor 240 at a moisture content sufliciently high that, aftercompaction and such reduction in moisture content as may be caused bycompaction, the web 222 will still have the 1:1, or greater, ratiorequired for machine glazing. Thus, the web 222, as shown in FIG. 2 maybe conducted to the compactor 240 directly from a wet press section witha water to fiber ratio of, say 2:1 or greater if the drying capacity ofthe particular Yankee section is high enough. If not, the web 222 may beconducted from the wet press section to one or more preliminary dryerdrums to bring the moisture content down to such a point that aftercompaction it will have a water to fiber ratio sufficiently high formachine glazing but not in excess of the capacity of the Yankee dryersection.

In FIGS. 1 and 2 respectively the compactors 40 and 240 are shown ascomprising elastomeric blankets 41 and 241, hard surface rolls 42 and242, idler rolls 43, 243, 44, 244, 45, 245 and optional auxiliary driverolls 60 and 260. The hard surface rolls 42 and 242 respectively aredriven rolls and the rolls 43 and 243. are nip rolls so mounted thattheir axes may be moved toward and from the hard surface rolls withwhich they are associated to adjust the amount of nip pressure exertedupon the elastomeric blankets 41 or 241 and upon the paper webs whichpass between the blankets and the hard surface rolls for the compactionthereof. The idler rolls 45 and 245 are usually bodily adjustable to putdesired tension upon the elastomeric blankets. It will be apparent thatthe compactors 40 and 240 as so far described are similar to one of theforms described in US Pat. No. 2,624,245 to S. L. Cluett.

In FIGS. 1 and 2 there is shown one optional feature which ordinarily isnot utilized in the commercial practice of prior art compacting. Thus,in these figures auxiliary drive rolls 60 and 260 respectively have beenillustrated as forming a nip with the idler rolls 44 and 244 for thepurpose of driving the elastomeric blankets 41 and 241 at a desiredlineal speed. Instead of the auxiliary rolls 6t and 260 the auxiliarydriving effect may be achieved by driving the nip roll 43 or 243 ofFIGS. 1 and 2 by suitable mean (not shown) which take into account thefact that the nip rolls also must be bodily movable to adjust nippressure. In many instances in the practice of the present inventionsome such auxiliary drive is ad visable or necessary because thesurfaces of the driven, hard surface rolls 42 and 242 have such low dragcharacteristics with respect to the moist webs 22 and 222 that slippingwill occur and the elastomeric blanket and the moist paper web adheredthereto would tend to move at too low a speed for proper operation. Theauxiliary drive rolls 60 and 260 or other auxiliary driving provisionsas noted above will assure proper blanket and Web speed under allconditions. In prior art compactors the auxiliary drive for the blankethas not been required since the hard surface elements of such compactorsat best have had frictional drag characteristics so high with respect tothe paper web that movement of the web and blanket at desired linealspeed was assured.

In FIG. 3 there is shown in enlarged detail the nip portion of acompactor 340 of the type used as the compactors 40 and 240 of FIGS. 1and 2 respectively. As is known from the prior art the compacting of afibrous web to enhance toughness and stretchability is accomplished byapplying simultaneously to the web forces which act in the planeparallel to the general web surfaces and in the plane normal to suchsurfaces. These forces push and crowd the fibers together to strengthenexisting bonds and to form additional bonds and adhesions between fibersand fibrils of the web in its compacted condition. In the figures of thedrawings the compactors act to shrink the web in a direction parallel toits travel through the machine and the finished web accordingly willexhibit greatest enhanced stretchability in this machine direction. Asbest seen in FIG. 3 the endless elastomeric blanket 341 which,typically, may comprise a strong, inextensible backing layer secured toa smooth-surfaced elastomeric paper engaging layer having a durometerhardness in the range from 40 to 60, wraps a substantial portion of theperiphery of the nip roll 343 as it approaches the hard surface roll342. Thus the paper engaging surface 346 of the blanket will be convexlycurved and stretched as it approaches the nip. The web 322 is broughtinto contact with the stretched surface 346 of the blanket just ahead ofthe nip between rolls 342 and 343. As the blanket and web enter the nipthe web is firmly pressed between the surface 346 of the blanket and thehard surface 347 of roll 342 and it will tend to adhere firmly to thestrectched elastomeric surface 346. As the web and blanket pass throughthe nip the blanket is so guided as to wrap the surface of the hardsurface roll 342. The resultant reversal of curvature of the elastomericsurface 346 causes it to relax and shorten and to correspondinglyshorten the web 322 which is firmly adhered to the surface 346 duringthe shortening thereof. The web is still pressed against the hardsurface 347 and it will be apparent that at some point within the nipthe web 322 must begin to slip and then continue to slip relative to thesurface 347 of hard surface roll 342 for such shortening to occur.

With specific reference to US Pat. 2,624,245, the process includesconfining the web between two moving elements, one of which has a webcontacting surface which is smooth and elastomeric and the other ofwhich has a web contacting surface which is hard and offers lowerfrictional resistance to movement of the web than does the surface ofsaid elastomeric element, and while the web is so confined contractingthe web contacting surface of said elastomeric element in order tocontract the web with it while said web is still confined against andslipping relative to said hard surface to thereby compress the web inthe direction of contraction of said web contacting surface so that thefibers and fibrils of the web are brought into such close contact witheach other that strong bonding and adhesions are produced therebetween.

As noted above it was thought that the moisture content of the web as itentered the nip of a compactor had to be below a certain level forvarious reasons including the constantly observed fact that when a webhad a moisture content above a water to fiber ratio of about 0.65:1 itwould stick to the surface 347 of the hard surface roll 342 and wouldnot follow the recoil of the surface 346 of the elastomeric blanket 341.When the Webs were only slightly too moist they would not be compactedbut simply would be scuffed as a result of slippage relative to theelastomeric blanket surface 346. At higher moisture contents the websfrequently were badly damaged or destroyed. In other words the webs didnot have suflicient strength in shear to overcome the static friction ofthe hard surface relative to the webs at such higher moisture contents.

The hard surface 347 of roll 342 always is maintained at a temperatureat or above the boiling point of water in prior-art operation in orderto promote slippage of the moist web relative to the hard surface. Inprior-art operations the hard surface usually was very smooth andusually was of polished chromium. The lubricating effect of steam due tothe temperature of the surface as well as the additional lubrication bysilicones, for example, which was sometimes provided, were essential topermit effective compression of webs at the relatively low moisturecontents heretofore regarded as the maximums for successful operation.

The present invention provides hard surfaces which may be heated butfrequently to much lower temperatures than in the prior art, which donot require additional lubricants for operation upon webs at moisturecontents as heretofore used and, most importantly, at moisture contentsexceeding and in many instances greatly exceeding the highest moisturecontents at which prior-art compression could be practiced. These hardsurfaces have coefficients of static friction, with respect to webs atsuch higher moisture contents which are low enough to permit slipping tostart within the nip at the proper time. Particular examples of suchsurfaces and the combinations of characteristics to guide those skilledin the art in selection of other surfaces suitable for use in thepresent invention will now be given.

A first suitable hard surface 347 may consist of a coating of Teflonfluorocarbon (TEE) resin (Du Pont) or similar resin applied to therelatively smooth surface of a metal roll 342. Such resins are availablein various grades and for the present purpose some of the grades mostrecently developed by the supplier for durability under abrasion andelevated temperature conditions are preferred. The resin coating shouldhave a thickness of about 0.002 inch or more when applied to a metalsurface. If the metal surface is somewhat roughened, as it may be toimprove adherence of the coating thereto, the coating should besufficiently thick that the surface thereof may be polished to desirablesmoothness while leaving a minimum thickness of about 0.002 inch.Thicker coatings of the presently-available Teflon resins are notnecessary or desirable although the constant efforts of the supplier (DuPont) to provide greater durability can be eX- pected to result inresins which can be used in thinner or thicker coatings for the presentpurposes.

A second suitable hard surface 347 for the roll 342 consists of acoating of resin, which may be a Teflon or similar resin as describedabove, applied over an etched or pitted metal surface of roll 342.Preferably the metal surface is a plating of chromium first polished toa smooth condition and then given a matte or pitted finish. With thematte finish the high spots are peaks. The pitted surface may be formedby blasting the polished plating with a suitable material such as glassbeads to form closely spaced indentations upon the surface, with thehigh spots being what remains of the original polished surface. Thematte or indented surface is then coated with a resin such as a Teflonfluorocarbon resin (TFE) (Du Pont) or other durable types of resin ofsuitable characteristics. The resin coat is thick enough to fill thevalleys of the matte or indented chromium base and of course will extendover the high portions as well. When a roll with such a surface is putinto use for the present invention the resin extending over the highportions will eventually wear away exposing the metal in such zones. Therate of wear thereafter will be progressively reduced as more of themetal high portions are exposed. The resin remaining in the valleys willstill constitute the major portion of the area of the surface wherebythe surface will continue to exhibit substantially the samecharacteristics as it would were it a smooth, polished surfaceconsisting solely of the resin.

Another, third, suitable surface for use in the present invention is oneconsisting entirely of metal which exhibits characteristics sufficientlysimilar to the resin surfaces of the first and second surfaces discussedabove to be entirely suitable for the present invention. Furthermore itis regarded as preferable over the first and second examples for thepractical reason that it will have a much longer useful life than theresin surfaces aforesaid since it should wear longer and is less likelyto be damaged. This third useful surface consists of a plating ofchromium or other suitable hard metal upon the base metal of the roll342. The plating preferably should be at least about 0.002 to 0.003 inchthick. The plating is treated or is so applied that the surface thereofis made up of small closely spaced convex nodules. One way to provide asurface of such conformation is to start with a roll 342 made of steelwhich is smooth or which has been polished to a very smooth condition.The steel surface is then blasted with suitable material to form closelyspaced indentations with intervening high portions. The blasted steelsurface is then plated with chromium which will form smoothly roundedconvex nodules where it extends over the high portions of the blastedsteel surface. Metal rolls of this general type with surfaces of variousdegrees of roughness may be obtained from Brame Textile Machine Companyof Greensboro, NC

For use in the present invention the surface texture of the third,nodular metal, hard surface 347 should show an average Roughness HeightR.M.S., of from about 40 to about rnicroinches determined in accordancewith ASA B46.l-1962 with a Roughness Width cutoff value of 0.100 inches.To achieve such texture the roughness of the blasted steel roll beforeplating and the thickness of the chromium plating must be chosen inrelation with each other in a manner known to those skilled in the art.

While the three examples of useful surfaces given above are quitedifferent in obvious respects they share certain characteristics whichappear to explain why they, in contrast to the surfaces heretofore usedin. the compacting of paper, make it possible to compact paper atmoisture contents substantially higher than those to which prior artcompacting has been limited. In a general sense these characteristicshave to do with the behavior of the surfaces not only with respect tothe water and to the wet fibers of which the wet fibrous web isprimarily composed, but more importantly, as the present inventor hasdiscovered, with respect to the wet fibrous sheet itself. For example ithas been recognized that the hard surface should be one that isdiflicult to wet with water, that is, the surface should exhibit arelatively high contact angle with water. Also, it has been recog nizedthat the hard surface should not tend to pick individual fibers from theweb under the conditions existing in the pressure nip of the compactor.Application of these recognized principles has led to some improvementin the compaction of paper at the moisture contents already in use, suchas the ability to operate at higher speeds, to achieve greatercompaction and to operate upon somewhat lighter-weight webs but have notpermitted operation on webs of significantly higher moisture content.

The point just discussed is exemplified by the results achieved bytesting a highly polished chromium surface against one that is lightlyblasted to a matte finish. A polished chromium surface having aRoughness Height Value of from 4 to 8 microinches R.M.S., typical of thesurfaces heretofore used in the compacting of paper, which has amoderately high contact angle with water was found by the presentinventor, in a series of tests which will be more fully described below,to pick a substantial quantity of paper fibers from a sheet of paperwith a water to fiber ratio, by weight, of about 3:1. Another chromiumsurface known to be useful in priorart compaction of paper, which hasbeen blasted to form an overall pattern of very small sharp peaks has acontact angle with water which was very much higher than the polishedsurface and it was found to exhibit no detectable tendency to pickfibers from a web of paper at the same water to fiber ratio of about3:1. However, such blasted surface, in spite of its high contact anglewith water and its freedom from fiber picking when used in a laboratorycompactor was not any more capable of use for compacting paper atmoisture contents of, say, a water to fiber ratio of about 3:1, than wasthe polished chromium surface. The laboratory tests conducted withlabora tory compactor equipment which had revealed the results juststated were then supplemented by a series of tests upon varioussurfacing materials and surface textures to determine thecharacteristics which were controlling as regards the behavior of thosesurfaces with highly moist webs. It was in such studies that it wasdiscovered that the static frictional characteristics of the surfacewith respect to a wet web were of much greater imporance than thedynamic frictional characteristics.

For the extended tests hand-sheets of paper were formed from pulp ofcarefully controlled uniformity and some of them were pressed to asubstantially uniform moisture content with a water to fiber ratio ofabout 3:1. Other sheets were dried to air dry condition. In addition tofiber picking tests with the wet sheets and contact angle measurementsfor each of the surfaces a series of tests were made to determinefrictional characteristics of both wet and dry sheets with the varioussurfaces.

The contact angle of each surface with water was measured by knowntechniques which, while not in accordance with any published standards,were carefully arranged so as to be uniform during this particularseries of observations.

Surface texture was determined, as noted above, in accordance with ASAB46.1 --1962 and Root Mean Square averages are reported herein withRoughness Width Cutoff of 0.100 inch. It will be appreciated, however,that analysis of surface texture in this manner does not give anyindication as to whether the surface protuberances are rounded or aresharp and accordingly Roughness Height is reported herein only inconnection with those surfaces which have the rounded, nodularprotuberances which the present inventor has found to be the best of theall-metal surfaces for use in the present invention. The RoughnessHeight of such surfaces was examined in order to establish a rangewithin which successful compaction of paper could be carried out atmoisture contents such as exist in paper coming from a Wet press or thewet press section of a paper making machine.

Fiber picking tests were made, using the wet hand sheets, but are notfully reported or described herein since picking of any significantamount was found only in connection with the polished chromium surface(RMS 4-8) of a type heretofore used for compacting of paper atcommercial moisture contents of 0.65:1 water to fiber ratio or less. Itshould be reported however that the preferred convex nodular metalsurfaces started to pick very slightly at Roughness Height values of RMS55 or less. This occurred with paper sheets at a Water to fiber ratio ofabout 3:1. For this reason as well as the fact that the coefiicient offriction-wet began to approach that of polished chromium as the nodularsurfaces became smoother, the lower limit on surface texture of theconvex nodular metal has been determined to be about 40 RMS. While thecomplete range is operative with the highest moisture contents thesmoother surfaces in such range are better adapted to operate with paperat the lower water to fiber ratios within the range of from about 1:1 toabout 3:1.

To determine the coefiicient of static friction of the various surfacesapparatus was employed to observe the angle of repose between thesurface under test and the hand sheets of paper, both wet and air-dry.The apparatus consisted of a table faced with plate glass and hinged atone end. The other end was arranged to be lifted at a controlled rate of0.5 per second by a hydraulic-pneumatic system. The paper sample wasclamped to the free end of the table and a flat plate having the surfaceunder test was laid, test surface down, upon the paper sample. The freeend of the table was then progressively elevated to incline it relativeto the horizontal. the angle at which slippage of the test plate underthe influence of gravity just starts is reported below as the angle ofrepose, which, for practical purposes is regarded as equivalent to theangle at which the onset of slipping is imminent. The tangent of theangle of repose is the coefficient of static friction.

A large number of hand-sheets was tested with each surface and theangles of repose and the coefficients of friction, reported below, arethe result of averaging the observations. The hand-sheets tested wereeach about 12" x 12" and the test plates each were 8" x 10 (surface) x1" thick. The test plates each weighed about 22.2 pounds whereby thepressure upon the paper sample was about 0.27 pound per square inch. Theangles of repose with respect to the air-dry paper samples were allquite low and did not difier a great deal whereby the coefficients offriction-dry are not reported below. The coefficients of friction-wetare reported below because of their evident significance.

In the condensed table below test results are set forth in connectionwith surfaces as follows:

(A) Polished chromium, 4-8 R.M.S. (B) Nodular chromium, 55 R.M.S.(multi-directional lay tolerance 50-60 R.M.S.)

(C) Nodular chromium, 125 R.M.S. (multi-directional lay tolerance -150R.M.S.) (D) Polished Teflon or similar resin coating on smooth metalbase. (E) Teflon or similar resin on pitted metal, after wear (F) Mattechromium, sharp peaks Surfaces'A and F are prior art compacting surfacesand are not useful in the present invention while surfaces B,

C, D and E are useful in this invention as described below.

TAB LE Moisture Coefficient Contact content Angle Angle of static angleof paper, repose repose friction, Surface H2O (deg) percent dry (deg)wet (deg) wet 64. 2 76. 2 20. 7 31. 1 60 77. 3 76. 9 l2. 7 25. S 48 78.9 76. 5 18. 8 23. 0 42 95. 1 76. 6 l7. 7 12. 3 22 95. l 75. 9 20. 7 13.3 24 101.8 77. 4 20.0 29. 8 57 ever, the angle of repose-wet withrespect to paper at a water to fiber ratio of about 3:1 for each ofsurfaces A and F is significantly higher than that angle for the othersurfaces. The Teflon or similar resin surfaces, polished solid resin insurface D and part-resin, part-metal in surface E, have angles ofrepose-wet which are very low, less than half that of the polished ormatte chromium surfaces A and F. It will be noted that the Teflon resinsurfaces D and B have lower angles of repose-wet than their angles ofrepose-dry due to the peculiar characteristics of resins of this generaltype.

The resin surfaces D and E are substantially identical incharacteristics reported in the table and either one may be used for thepresent invention. Surface E is preferred because of its greaterdurability. Surface E was also tested before being worn down to anextent such as to expose substantial portions of the high spots of thebase metal and it exhibited substantially identical characteristics. Thesurface appearance before wear was quite similar to the polished surfaceof surface D. Accordingly a Teflon or similar resin coated, blasted oretched, metal base roll may be put into immediate use in the presentinvention and it eventually will wear into a smooth partresin,part-metal surface of good durability.

The convex nodular metal surfaces B and C, as shown in the table aboveboth have angles of repose-wet which are higher than those of the resinor part resin surfaces but which are nevertheless significantly lowerthan the prior art compacting surfaces A and F. Surface C, with a finishof 125 microinches R.M.S. has a lower angle of repose-wet than thesmoother surface B but both are entirely useful for compacting paper atwater to fiber ratios of about 3 :1 as well as papers at any lowermoisture contents including those employed in the prior art. The upperlimit of surface roughness of these convex nodular metal surfacesappears to be established as a practical matter by the belief that therougher surfaces may have a tendency to mark the paper. The upper limitof 175 microinches R.M.S. has been selected on this basis and roughersurfaces, if they olfer any advantage in special cases, may be used solong as marking does not become objectionable.

'From the table above it will be apparent that the frictionalcharacteristics of a surface with respect to a dry Web, such as paper orplastic films, can not serve as a guide for determining whether asurface is suitable for the present invention. For example whilesurfaces A, C, E and F have very similar angles of repose-dry theydiffer very sharply in angles of repose-wet and only those with thelower angles of repose-wet are useful in the present invention. Thecoefiicients of static friction-wet calculated from the observed anglesare believed by the present inventor to represent a way to give anumerical value to the relative frictional drag of a surface withrespect to a wet web of paper. Taking the coefficient of staticfriction-wet of surface A which is a surface known to be unfitted foruse in the present invention and assigning it the arbitrary percentagevalue of 100 the relative values of the remaining surfaces areapproximately as follows: E, 82%; C, 70%; D, 37%; E, 40%; F, 95%. Thesenormalized values thus afford a convenient way of expressing therelative drag of the several surfaces with respect to a wet paper web ata water to fiber ratio of about 3:1 from which it reasonably can beconcluded that surfaces having a frictional drag about 85%, or less,that of the relative drag of polished chromium are useful in the presentinven tion. Another way of expressing the effective relative frictionaldrags of these surfaces with respect to a wet web is to use thecalculated coeflicients of static frictionwet. From the table it will beapparent that such coefiicient should not exceed about 0.5.

The use of the low frictional drag surfaces provided by the presentinvention is not limited to compactors in which the elastomeric elementis an endless belt such as the belts 41, 241 and 341 illustrated in thedrawings. In another well known form of compactor the elastomericelement consists of a rubber, or equivalent, jacket applied to the niproll which otherwise corresponds with the nip rolls 43, 243 and 343.Also it is known to drive the hard surface roll corresponding with thehard surface rolls 42, 242 and 342 at a surface speed somewhat in excessof the surface speed of the elastomeric element whether the latter is abelt as illustrated herein or is a jacket on the nip roll as justdescribed. In all cases the low frictional drag of the hard surfacesprovided by the present invention gives the advantage of providingimproved compacting in the pressure nip at the moisture levels of theprior art while also giving the unique advantage of permittingcompacting of paper webs in the pressure nip at much higher moisturecontents, for example up to a water to fiber ratio by weight of about3:1.

As can be seen from the foregoing description of preferred forms of thepresent invention an important aspect of the invention is that ratherthan being limited by the moisture content of the web the ability tocompact is limited only by the ability to adjust properly thecharacteristics of the hard surface roll of the compactor. Al though itis not intended that this invention shall be limited to any specifictheory it is believed that a substantial amount of original bonding hasoccurred between fibers and that sufficient voids exist between fibersfor inter-fiber movement at the moisture contents at which paper webstypically leave a wet press or the wet press section of a papermakingmachine. The forces exerted by the surface tension of the water upon thefibers becomes very great when air strikes through the mat before itleaves the forming screen and the water consequently changes fromcontinuous to discontinuous phase, whereby there may be substantialbonding of the fibers at this point. In any event the wet press orpresses probably form more fiber bond and certainly reduce the moisturecontent to create more voids.

What is claimed is:

1. The process of producing a web of adherent waterlaid cellulose fibershaving substantial permanent extensibility in excess of that of the webas laid, and which has no substantial decrease in thickness whenstretched, consisting of the steps of: confining the webat a point inits manufacture when its moisture content expressed as a ratio of waterto fiber by Weight is the range of from about 1: 1 to about 3:1, betweentwo moving elements, one of which has a web contacting surface which issmooth and elastomeric and the other of which has a web contactingsurface which is hard and offers lower frictional resistance to movementof the web than does the surface of said elastomeric element, the webcontacting surface of said other element having small nodularprotuberances on the surface of said hard roll, said protuberanceshaving smoothly rounded convex configurations and said protuberancesbeing closely spaced, and while the web is so confined contracting theweb contacting surface of said elastomeric element in order to contractthe web with it while said web is still confined against and slippingrelative to said hard surface to thereby compress the web in thedirection of contraction of said web contacting surface so that thefibers and fibrils of the web are brought into such close contact witheach other that strong bonding and adhesions are produced therebetween,and then passing the web to a Yankee drying cylinder at a water to fiberratio of at least about 1:1 and adhering the web to the surface thereofwhile the web is still in the condition of its emergence from thecompactor whereby the web is dried and glazed on one of its surfaces.

2. The process of producing a web of adherent waterlaid cellulose fibershaving substantial permanent extensibility in excess of that of the webas laid, and which has no substantial decrease in thickness whenstretched, consisting of the steps of: confining the web at a point inits manufacture when its moisture content expressed as a ratio of waterto fiber by weight is in the range of from about 1:1 to about 3:1,between two moving elements, one of which has a web contacting surfacewhich is smooth and elastomeric and the other of which has a webcontacting surface which is hard and offers lower frictional resistanceto movement of the web than does the surface of said elastomericelement, the web contacting surface of said other element comprising alayer of hard metal plating on the surface thereof, the layer ofchromium having closely spaced indentations and a layer of resin beingsufiiciently thick to fill in all the indentation and extending over thehigh portions as well as the indentation, and while the web is soconfined contracting the web contacting surface of said elastomericelement in order to contract the web with it while said web is stillconfined against and slipping relative to said hard surface to therebycompress the web in the direction of contraction of said web contactingsurface so that the fibers and fibrils of the web are brought into suchclose contact with each other that strong bonding and adhesions areproduced therebetween, and then passing the web to a Yankee dryingcylinder at a water to fiber ratio of at least about 1:1 and adheringthe web to the surface thereof while the web is still in the conditionof its emergence from the compactor whereby the web is dried and glazedon one of its surfaces.

3. A machine glazingapparatus and a Yankee drier for machining glazing aweb of paper wherein the compacting apparatus includes a pressure nip inwhich the web of paper is supported by an elastic surface which pressesthe web against the surface of a hard roll while the web is slidingrelative to the surface of the hard roll, said hard roll having: smallnodular protuberances on the surface, said protuberances having smoothlyrounded convex configurations of a size and spacing that the surfacewhich they form has a Roughness Height R.M.S. with Roughness Widthcutoff of about 0.100 inch, of from about 40 to about 175 microinchesand wherein said Yankee drier immediately follows said compactingapparatus.

4. The apparatus of claim 3 wherein the nodular protuberance of saidhard roll consist of a chromium layer on a pitted metal base.

5. The apparatus of claim 4 and including a layer of resin on thesurface of said roll.

References Cited UNITED STATES PATENTS 2,114,072 4/1938 Cleveland 162358XR 2,624,245 1/ 1953 Cluett 162206 XR 3,011,545 12/1961 Welsh et al162-206 XR 3,290,209 12/1966 Ihrrnan 162361 3,362,869 1/1968 Welsh162-206 XR S. LEON BASHORE, Primary Examiner R. H. TUSHIN, AssistantExaminer US. Cl. X.R. 2618.6; 162361

